Ion exchange systems are well-known in the prior art. Such systems typically include a pressure vessel in which a bed of resin is supported. The resin material facilitates the ion exchange process and must be periodically replenished or "regenerated". Thus in operation the systems have two major cycles of operation, a production cycle in which the raw water or other feed is treated and then exhausted from the vessel, and a regeneration cycle, during which a regenerant is provided to the vessel to replenish the resin. Such operational modes are further characterized in the art as either cocurrent or countercurrent. In a cocurrent mode, downflow is employed for both the production and the regeneration cycles. In the countercurrent mode, the regenerant is applied in a flow opposite from the production cycle feed flow. Prior art countercurrent systems have been built with the regenerant applied upflow or downflow.
The prior art ion exchange systems have many shortcomings. Cocurrent operation leaves a residue of ions from the previous regeneration. Thus, following regeneration, the lowest quality resin is at the bottom of the vessel adjacent the exhaust, precisely where the best quality resin is needed most for the next production cycle. Countercurrent operation solves this problem to enable the best quality resin (following regeneration) to be adjacent the exhaust. On the other hand, by its very nature countercurrent operation creates a fluidized bed during the regeneration cycle. Thus the prior art has developed several somewhat costly and complicated techniques to hold the resin bed in place during regeneration. Typically this has been accomplished through use of a counterflow of water or gas above the bed, or through use of inert fillers above the bed. While systems employing countercurrent operation have better production efficiency and higher product quality than cocurrent systems, there still remains a long-felt need in the ion exchange art to enhance the performance of such prior art systems.